Add maximum FPS option to LGraphCanvas

[webfiltered]

FPS cap

Adds an property to LGraphCanvas to specify maximum render frames per second.

Currently, the only limit to FPS is the refresh rate of the screen, reported by the browser. Users with very high refresh rates experience unnecessarily high GPU usage.

Usage:

// Limit FPS to 30
canvas.maximumFps = 30

// Existing behaviour (Default):
canvas.maximumFps = 0